U.S. patent application number 11/528411 was filed with the patent office on 2008-03-27 for process for maleating polymerization residues and products.
Invention is credited to Jeffrey A. Jones, Chun D. Lee.
Application Number | 20080076875 11/528411 |
Document ID | / |
Family ID | 39225866 |
Filed Date | 2008-03-27 |
United States Patent
Application |
20080076875 |
Kind Code |
A1 |
Lee; Chun D. ; et
al. |
March 27, 2008 |
Process for maleating polymerization residues and products
Abstract
A process for converting distillation residues obtained from
polymerization processes to useful maleated products is
provided.
Inventors: |
Lee; Chun D.; (Cincinnati,
OH) ; Jones; Jeffrey A.; (Morrow, OH) |
Correspondence
Address: |
William A. Heidrich;Equistar Chemicals, LP
11530 Northlake Drive
Cincinnati
OH
45249
US
|
Family ID: |
39225866 |
Appl. No.: |
11/528411 |
Filed: |
September 27, 2006 |
Current U.S.
Class: |
525/71 |
Current CPC
Class: |
C08F 6/28 20130101; C08F
255/02 20130101; C08F 6/28 20130101; C08F 255/02 20130101; C08L
51/06 20130101; C08F 222/06 20130101 |
Class at
Publication: |
525/71 |
International
Class: |
C08L 51/04 20060101
C08L051/04 |
Claims
1. A process for the maleation of distillation residues obtained
from high molecular weight ethylene polymer polymerizations
comprising: (a) treating the distillation residue to remove
substantially all of the hydrocarbon diluent; (b) incorporating 1
to 10 weight percent maleic anhydride, based on the weight of the
distillation residue; (c) incorporating 0.25 to 6 weight percent
organic peroxide, based on the weight of the distillation residue;
(d) heating the mixture above the decomposition temperature of the
organic peroxide until substantially all of the maleic anhydride is
reacted; and (e) recovering the maleated product.
2. The process of claim 1 wherein the distillation residue contains
4 to 10 weight percent hydrocarbon diluent, 5 to 20 weight percent
high molecular weight high density polyethylene, 60 to 90 weight
percent low molecular weight polyethylene waxes and 0.2 to 1 weight
percent catalyst residue.
3. The process of claim 2 wherein the hydrocarbon diluent is
hexane, the high molecular weight high density polyethylene has a
density of 0.940 to 0.955 g/cm.sup.3 and melt index of 0.02 to 0.3
and the molecular weight of the polyethylene waxes is from about
100 up to about 30000.
4. The process of claim 2 wherein (a) is conducted at a temperature
in the range 120.degree. C. to 150.degree. C.
5. The process of claim 4 wherein the residue treated in accordance
with (a) contains less than 200 ppm hydrocarbon.
6. The process of claim 2 wherein the maleic-anhydride
incorporation is carried out in the melt state.
7. The process of claim 6 wherein the amount of maleic anhydride
incorporated is from 1.5 to 8 weight percent.
8. The process of claim 2 wherein the organic peroxide
incorporation is carried out in the melt state at a temperature
below the decomposition temperature of the organic peroxide.
9. The process of claim 8 wherein the amount of the organic
peroxide incorporated is from 0.5 to 5 weight percent.
10. The process of claim 2 wherein the (d) is conducted at a
temperature in the range 103.degree. C. to 200.degree. C.
11. The maleated product produced by the process of claim 1 which
contains from 0.5 to 7 weight percent bound maleic anhydride.
12. The maleated product of claim 11 further characterized by
having a viscosity which is essentially shear dependent.
13. A process for the maleation of distillation residues obtained
from a process for the polymerization of high molecular weight high
density polyethylene, said distillation residue containing 4 to 10
weight percent hydrocarbon diluent, 5 to 20 weight percent high
molecular weight high density polyethylene, 60 to 90 weight percent
low molecular weight polyethylene waxes and 0.2 to 1 weight percent
catalyst residue, comprising: (a) heating said residue at a
temperature of 120.degree. C. to 150.degree. C. to remove
substantially all of the hydrocarbon diluent; (b) maintaining the
essentially hydrocarbon diluent-free residue obtained from (a) in a
molten state and incorporating from 1 to 10 weight percent maleic
anhydride; (c) incorporating 0.25 to 6 weight percent organic
peroxide into the melt containing the maleic anhydride from (b)
while maintaining the temperature of said melt below the
decomposition temperature of the organic peroxide; (d) increasing
the temperature of the mixture from (c) above the decomposition
temperature of the organic peroxide and maintaining until
substantially all the maleic anhydride is reacted; and (e)
recovering the maleated product.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The invention relates to a process for converting
distillation resides obtained from polymerization processes to
useful products. More specifically, the process is directed to the
maleation of distillation residues to produce maleated products
characterized by having viscosities which are shear dependent.
[0003] 2. Description of the Prior Art
[0004] High density polyethylene (HDPE) resins are widely utilized
for film applications such as for grocery sacks, merchandise bags,
can liners and the like. HDPEs are typically produced by
copolymerizing ethylene with a minor amount of a C.sub.3-8
.alpha.-olefin comonomer using either Ziegler-Natta catalysts or
the so-called Phillips catalysts. The latter are chromium oxide
catalysts and generally produce HDPE resins having broad molecular
weight distributions (MWDs) whereas Ziegler-Natta catalysts, which
are based on transition metal technology, produce narrower MWD
HDPEs.
[0005] While most HDPEs exhibit good tensile and stiffness
properties, certain improvements, such as increased tear properties
and increased impact strength, can be achieved by increasing the
molecular weight of the resin. High molecular weight resins are,
however, more difficult to process for film production and require
the use of higher processing temperatures and/or pressures. To
ameliorate this effect, high molecular weight high density
polyethylene (HMW HDPE) film grade resins preferably have broad
MWDs.
[0006] Multiple-stage polymerization technologies wherein polymers
of different molecular weights are produced in separate reactors
and blended to produce a final resin product are a known means of
producing resins having broadened MWDs (see e.g., U.S. Pat. No.
5,236,998)
[0007] U.S. Pat. No. 4,357,448 discloses a process wherein ethylene
or a mixture of ethylene and a small amount of another
.alpha.-olefin are polymerized in two successive steps under
different hydrogen partial pressures using high activity
Ziegler-type catalysts to produce HDPE resins having broad MWDs. A
similar procedure for the production of high molecular weight
medium density polyethylene resins is disclosed in U.S. Pat. No.
6,770,715.
[0008] In one mode of operation for the production of HMW HDPEs
where successive polymerization steps are employed, ethylene is
homopolymerized in a first reactor in a hydrocarbon diluent, such
as hexane or heptane, and the amount of molecular weight regulator,
i.e., hydrogen, is maintained at low levels to maximize molecular
weight of the homopolymer formed. The high molecular weight
homopolymer produced in the first reaction zone is then fed along
with the solvent and catalyst to a second reaction zone where
ethylene and a C.sub.3-8 .alpha.-olefin comonomer are copolymerized
in the presence of the homopolymer. The ratio of homopolymer
produced in the first reactor to copolymer produced in the second
reactor (which typically has a lower molecular weight) is selected
to provide the desired average molecular weight and MWD in the
final resin product for optimal physical properties and processing
characteristics.
[0009] While such processes are an effective and versatile means
for producing a broad array of HMW HDPE resins of varying densities
and melt indexes (MIs), substantial amounts of low molecular weight
polymers (LMWPs) are also formed. The LMWPs have number average
molecular weights (M.sub.n) from several hundred up to about 30000
and, more typically, up to about 20000. These low molecular weight
by-product polymers have a waxy character and they remain in the
hydrocarbon diluent after separation and recovery of the HMW HDPE
by centrifugation or other suitable means.
[0010] In a typical HMW HDPE operation, the hydrocarbon diluent
containing the LMWP, any unrecovered HMW HDPE and catalyst residue
is subjected to one or more distillations to recover the
hydrocarbon which is recycled for reuse in the polymerization
process. The still "bottoms" obtained from the distillation, also
referred to herein as the polymerizer/polymerization residue or
by-product, generally contain about 60 to 90 weight percent (wt. %)
LMWP, 5 to 20 wt. % HMW HDPE, 4 to 10 wt. % hydrocarbon diluent and
0.2 to 1 wt. % catalyst residue and catalyst deactivating agents,
e.g., alcohols.
[0011] Even though the low molecular weight ethylene polymer waxes
are the major constituents, these polymerizer residues cannot be
used as such for most wax applications due to the presence of
significant levels of the high molecular species (which increase
the viscosity to a level outside the useful range for most wax
applications) and their high metals content due to the presence of
catalyst residues (which form undesirable color bodies).
[0012] Since separation of the low and high molecular weight
species and removal of catalyst residues is difficult and not
economically feasible, it would be highly desirable if a process
were available whereby the polymerization residues recovered from
such processes could be effectively treated and converted into
useful products. These and other advantages are achieved with the
process of the present invention which is described in detail to
follow.
SUMMARY OF THE INVENTION
[0013] The invention relates to a process for maleating by-products
recovered from HMW HDPE polymerizations. In addition to converting
by-products to useful products the maleated wax products produced
by the process exhibit unexpected viscosity characteristics.
[0014] The process of the invention comprises treating a
distillation residue obtained from a HMW HDPE polymerization
processing containing 4 to 10 weight percent hydrocarbon diluent, 5
to 20 weight percent high molecular weight high density
polyethylene, 60 to 90 weight percent low molecular weight
polyethylene waxes and 0.2 to 1 weight percent catalyst residue to
remove substantially all of the hydrocarbon diluent incorporating 1
to 10 weight percent maleic anhydride, based on the weight of the
distillation residue; incorporating 0.25 to 6 weight percent
organic peroxide, based on the weight of the distillation residue;
heating the mixture above the decomposition temperature of the
organic peroxide until substantially all of the maleic anhydride is
reacted; and recovering the maleated product. Products produced by
the maleation process contain from 0.5 to 7 weight percent reacted
maleic anhydride and have a viscosity which is essentially shear
independent.
[0015] In a preferred mode of operation, the maleation is conducted
by (a) heating the distillation residue at a temperature of
120.degree. C. to 150.degree. C. to remove substantially all of the
hydrocarbon diluent; (b) maintaining the essentially hydrocarbon
diluent-free residue obtained from (a) in a molten state and
incorporating from 1 to 10 weight percent maleic anhydride; (c)
incorporating 0.25 to 6 weight percent organic peroxide into the
melt containing the maleic anhydride from (b) while maintaining the
temperature of said melt below the decomposition temperature of the
organic peroxide; (d) increasing the temperature of the mixture
from (c) above the decomposition temperature of the organic
peroxide and maintaining until substantially all of the maleic
anhydride is reacted; and (e) recovering the maleated product.
DETAILED DESCRIPTION OF THE INVENTION
[0016] The present process is directed to a method of utilizing
by-products obtained from processes wherein ethylene is polymerized
using Ziegler-Natta catalysts in a hydrocarbon medium. More
specifically, it relates to a process wherein distillation residues
obtained from multi-stage HMW HDPE polymerizations are maleated to
produce useful products. The by-products treated in accordance with
the process of the invention are comprised of about 60 to 90 wt. %
LMWPs, about 5 to 20 wt. % HMW HDPE, about 4 to 10 wt. %
hydrocarbon diluent and about 0.2 to 1 wt. % catalyst residue.
Catalyst residues include metal complexes, salts, etc., formed
during polymerization or as a result of catalyst deactivation
procedures prior to distillation, e.g., by the addition of alcohols
or ketones to "kill" the catalyst. Octanol is commonly used to
deactivate the catalyst in these types of polymerizations. If this
is the case, the residue may contain up to about 500 ppm residual
octanol. The amount of catalyst residue is determined utilizing
known x-ray fluorescence (XRF) procedures.
[0017] The distillation by-products utilized for the process of the
invention are residues obtained from processes wherein a first
ethylene polymer (homopolymer or copolymer) is produced in a first
polymerization zone and a second ethylene-.alpha.-olefin copolymer
resin is produced in a second polymerization zone in the presence
of the first ethylene polymer. The first and second polymers are
produced in the desired ratio to obtain a final HMW HDPE resin
product. The polymerizations are conducted in an inert hydrocarbon
medium in separate reactors connected in series using Ziegler-Natta
catalysts. Polymer produced in the first reactor is fed into the
second reactor with the catalyst, solvent and unreacted ethylene
where comonomer and additional ethylene are added. Such two-stage
processes are known and described in U.S. Pat. No. 4,357,448
details of which are incorporated herein by reference.
[0018] Typically, the amount of comonomer present in the first
reactor is very low and, in commercial operations, is the result of
the introduction of recycled gases and hydrocarbon diluent which
can contain comonomer.
[0019] The polymerizations are carried out in an inert hydrocarbon
medium using conventional Ziegler-type catalysts. Typically, the
same catalyst is used for both polymerizations; however, this is
not necessary. It may be desirable to add additional catalyst to
the second reactor and this catalyst may be the same or different
than the catalyst employed in the first reactor. Inert hydrocarbons
which can be used for the process include saturated aliphatic
hydrocarbons such as hexane, isohexane, heptane, isobutane and
mixtures thereof. Catalysts are typically metered into the reactors
dispersed in the same hydrocarbon used as the polymerization
medium. Hydrogen may be included in either or both of the reactors
to regulate molecular weight.
[0020] In one highly useful mode of operation, higher density,
higher MI polymer, predominantly ethylene homopolymer, is produced
in the first reactor and lower density, lower MI ethylene/butene-1,
ethylene/hexene-1 or ethylene/octene-1 copolymer is produced in the
second reactor. To accomplish this, hydrogen to ethylene mole
ratios from 1 to 10 are employed in the first reactor whereas
hydrogen to ethylene mole ratios from 0.01 to 1 are employed in the
second reactor. When operating in series mode, it may be necessary
to vent hydrogen prior to transferring the first polymer in order
to achieve the desired hydrogen:ethylene ratio in the second
reactor. This can be readily accomplished by means of a flash tank
installed between the two reactors.
[0021] MI and density of the first polymer produced in the first
reactor will be in the range 1 to 1000 g/10 min and 0.955 to 0.975
g/cm.sup.3, respectively, whereas MI and density of the second
copolymer produced in the second reactor will be in the range 0.001
to 10 g/10 min and 0.915 to 0.940 g/cm.sup.3, respectively. In a
particularly advantageous embodiment of the invention copolymer
produced in the second reactor will have a density of 0.925 to
0.938 g/cm.sup.3 and MI from 0.01 to 5 g/10 min.
[0022] Polymerizations in the first and second reactors are
generally carried out at pressures up to 300 psi and temperatures
up to 100.degree. C. Polymerization temperatures are most typically
maintained at 60.degree. C. to 95.degree. C. and, more preferably,
between 65.degree. C. and 85.degree. C. Pressures are most
generally maintained between 80 psi and 200 psi and, more
preferably, from 80 psi to 160 psi when using hexane(s) as the
polymerization medium.
[0023] Properties of the final HMW HDPE resin product will vary
depending on the properties of the first polymer and second
copolymer products produced in the respective reactors and the
ratio of first polymer and second copolymer resin components, i.e.,
composition ratio. The final HMW HDPE resin will, however,
generally have a density of 0.940 to 0.955 g/cm.sup.3 and MI from
0.01 to 0.5 g/10 min. Densities of the HMW HDPE resins produced by
the process are preferably in the range 0.945 to 0.952 g/cm.sup.3
and MIs are preferably in the range 0.02 to 0.3 g/10 min. Densities
and MIs referred to herein are determined in accordance with ASTM D
1505 and ASTM D 1238-01, condition 190/2.16, respectively. The HMW
HDPE resins generally have MWDs (M.sub.w/M.sub.n) in the range 20
to 30.
[0024] High activity Ziegler-Natta catalyst systems employed for
the polymerizations comprise a solid transition metal-containing
catalyst component and organoaluminum co-catalyst component. The
solid transition metal-containing catalyst component is obtained by
reacting a titanium or vanadium halogen-containing compound with a
reaction product obtained by reacting a Grignard reagent with a
hydropolysiloxane having the formula
R a H b SiO 4 - a - b 2 ##EQU00001##
wherein R represents an alkyl, aryl, aralkyl, alkoxy, or aryloxy
group as a monovalent organic group; a is 0, 1 or 2; b is 1, 2 or
3; and a+b<3) or a silicon compound containing an organic group
and hydroxyl group in the presence or absence of an
aluminum-alkoxide, aluminum alkoxy-halide halide or a reaction
product obtained by reacting the aluminum compound with water.
[0025] Organoaluminum co-catalysts correspond to the general
formula
AlR.sup.1.sub.nX.sub.3-n
wherein R.sup.1 is a C.sub.1-C.sub.8 hydrocarbon group; X is a
halogen or an alkoxy group; and n is 1, 2 or 3. Useful
organoaluminum compounds of the above type include
triethylaluminum, tributylaluminum, diethylaluminum chloride,
dibutylaluminum chloride, ethylaluminum sesquichloride,
diethylaluminum hydride, diethylaluminum ethoxide and the like.
[0026] High activity catalyst systems of the above types which can
be employed are known and are described in detail in U.S. Pat. No.
4,357,448, which is incorporated herein by reference.
[0027] The HMW HDPE polymer is typically recovered from the
hydrocarbon diluent by centrifugation although other means, such as
the use of Zig-Zag separators, may also be employed to separate the
polymer particles from the hydrocarbon medium. Although the bulk of
the high molecular weight resin is recovered, a small amount
remains with the hydrocarbon. Substantial amounts of LMWP formed
during the polymerization are also present in the hydrocarbon
diluent as are catalyst and any modifiers which may have been used
for the polymerization.
[0028] The hydrocarbon diluent containing the above components, the
amounts of which will vary depending on the mode of recovery used
and other operational variables, is subsequently distilled to
remove/recover the hydrocarbon which is recycled for use in the
process. Since in the preferred mode of operation, it is customary
to deactivate or "kill" any catalyst present in the hydrocarbon
prior to distillation, e.g., by the addition of alcohols or
ketones, species formed as a result of this procedure as well as
any residual deactivating agent (alcohol or ketone) will also be
present in the hydrocarbon diluent being distilled. Distillation
can be accomplished in a single distillation column but, more
typically, multiple stills are employed. Typically the recovered
hydrocarbon is purified and recycled to the first polymerization
reactor; however, the recycle stream may be split and introduced at
several points in polymerization sequence.
[0029] The distillation residue, i.e., the still bottoms remaining
when distillation is complete, are maleated in accordance with the
process of the invention. These residues will typically contain a
small amount of residual hydrocarbon (usually about 4 to 10 wt. %),
some unrecovered HMW HDPE polymer (usually about 5 to 20 wt. %) and
0.2 to 1 wt. % catalyst residue. The latter are various metal
species, i.e., complexes and salts, formed during polymerization
and upon treatment with the deactivating agent. Small amounts of
deactivating agents, typically less than 500 ppm, may also be
present. The bulk of the distillation residue, however, consists of
low molecular weight polymers produced during the polymerization.
These LMWPs, which have molecular weights in the range generally
associated with polyethylene waxes, comprise about 60 to 90 wt. %
of the residue. Molecular weights of the low molecular weight waxy
materials range from about 100 up to about 30000 and, more
typically, are in the range 100 to 20000. Molecular weights
referred to herein are number average molecular weights
(M.sub.n).
[0030] The distillation residues are maleated, i.e., reacted with
maleic anhydride, in accordance with the process of the invention
to obtain useful maleated products. The maleated products
containing both low and high molecular weight ethylene polymer
species possess unique viscosity characteristics rendering them
useful for a variety of applications but particularly as
compatibilizing/coupling agents for composites.
[0031] For the maleation process, the distillation residue is first
treated to remove substantially all of the remaining hydrocarbon.
This can be conveniently accomplished utilizing known
devolatilization procedures wherein the residue is heated above the
boiling point of the hydrocarbon. Removal of volatiles, i.e., the
hydrocarbon, is generally further facilitated by sweeping an inert
gas over and/or through the product, pulling a vacuum on the system
or by similar means. Commercial evaporators/devolatilizers are
known for these procedures. The temperature used for the
devolatilization will vary depending on the hydrocarbon. When the
hydrocarbon is hexane, widely used as a diluent for polymerization
processes of the type described above to produce HMW HDPE,
temperatures in the range 120.degree. C. to 150.degree. C. will
generally be used for the devolatilization step. Excessive heat
should be avoided to minimize polymer degradation. The devolatized
residue should be substantially hydrocarbon free, i.e., contain
less than about 200 ppm hydrocarbon and, more preferably, less than
50 ppm hydrocarbon.
[0032] The substantially hydrocarbon free residue may be stored at
this point or, as is more usually the case, passed directly to the
next step in the process where maleic anhydride is added and
incorporated. Any means suitable to uniformly distribute the maleic
anhydride in the devolatilized residue can be employed. This can be
accomplished in a suitable blender/mixer or in an extruder with a
suitable mixing chamber. The maleic anhydride can be dry blended
with the residue, such as in the case where it has been stored
after devolatilization; however, maleic anhydride incorporation is
preferably carried out in the melt state, i.e., the maleic
anhydride is added to and uniformly mixed into molten devolatized
residue. Temperature of the melt is preferably the same as that
employed for the devolatization step. The amount of maleic
anhydride incorporated will range from 1 to 10 wt. % and, more
preferably, is from 1.5 to 8 wt. %.
[0033] After incorporating the maleic anhydride, 0.25 to 6 wt. %
and, more preferably, 0.5 to 5 wt. % of an organic peroxide is
added to the molten mixture. The peroxide is preferably added at a
temperature below its decomposition temperature and this
temperature maintained until the peroxide is uniformly distributed
throughout the mixture. At that point the temperature is raised
above the decomposition temperature of the organic peroxide and
maintained until substantially all of the maleic anhydride is
reacted. The maleated product will contain from 0.5 to 7 wt. % and,
more preferably, from 1 to 5 wt. % bound maleic anhydride. The
extent of reaction, i.e., grafting, is determined using known
Fourier transform infrared spectroscopic (FTIR) techniques.
[0034] Organic peroxides and hydroperoxides which decompose at
temperatures below the melting point of the mixture can be used.
Suitable organic peroxides include dicumyl peroxide, dibenzoyl
peroxide, di-t-butyl peroxide, t-butylperoxybenzoate,
2,5-dimethyl-2,5-di(t-butylperoxy)hexane, t-butyl
peroxyneodecanoate, 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne,
t-amyl peroxypivalate, 1,3-bis(t-butylperoxyisopropyl)benzene, and
the like. Hydroperoxides can include di-t-butyl hydroperoxide,
t-butyl hydroperoxide and the like.
[0035] The reaction step can conveniently be carried out in the
same equipment used for the devolatilization and/or maleic
anhydride incorporation steps, e.g., using an extruder having a
mixing zone suitable for incorporating the maleic anhydride
followed by one or more reaction zones where maleation can occur.
Such extruders would have suitable screw designs and temperature
profiles and be appropriately configured. Other equipment such as
that manufactured by LIST USA INC. which incorporates a
devolatilizer with a kneader reactor could also be employed to
perform all three steps of the process in one continuous
operation.
[0036] Temperatures between about 130.degree. C. to 200.degree. C.
and, more preferably, from about 140.degree. C. to 180.degree. C.
are employed for the reaction step. Reaction times will vary
depending on the reaction conditions and the particular organic
peroxide used. Conditions should be such that substantially all of
the maleic anhydride is reacted. For batch operations reaction
times typically range from 3 minutes to 1 hour and, more
preferably, from about 10 to 40 minutes. For continuous operations,
such as where the reaction is carried out in an extruder with
highly efficient mixing and capable of operating at relatively high
temperatures, residence times can vary from 0.5 to 5 minutes.
[0037] Maleated products of the invention can be utilized in most
application where functionalized ethylene polymers are been used.
They are, however, particularly advantageous as
compatibilizing/coupling agents for wood-plastic composites (WPCs).
Use of cellulosic-reinforced plastic composites has grown in recent
years as consumers discover the advantages of these products
compared to wood. WPCs are increasingly being utilized for
installations in environments which are unfavorable to the use of
wood, e.g., where cracking, warping, rotting or attack by insects
would typically be expected.
[0038] Numerous plastic resins including HDPE, PVC, EVA, ABS and
polystyrene can be used with various cellulosic fillers for the
production of useful WPCs. The amount of cellulosic filler used
will vary depending on the particular resin and filler being used
and the intended application. In general, however, about 40 to 60%
cellulosic filler is utilized for extruded profiles whereas lower
filler loadings, on the order of 20 to 30%, are used for molded
pieces.
[0039] The maleated products of the invention are particularly
useful for composites comprised of 35 to 85 wt. % and, more
preferably, 40 to 80 wt. % matrix polymer and 15 to 65 wt. % and,
more preferably, 20 to 60 wt. % cellulosic filler. The maleated
distillation residues produced in accordance with the process of
the invention are utilized at levels of 0.5 to 20 wt. % and, more
preferably, from 1 to 10 wt. % to facilitate processing,
incorporation and binding of cellulosic filler materials.
[0040] Useful cellulosic materials can be any of the known products
available from a variety of natural sources or as by-products from
various processes. These can include such diverse materials as
paper, cardboard, wheat pulp, rice hulls, coconut shells, peanut
shells, corn cobs, sawdust, wood chips, wood fiber, wood flakes,
wood flour, ground wood, palm fiber, bamboo fiber, bagasse, jute,
flax and the like. Of these, wood fillers are particularly
useful.
[0041] In one highly useful embodiment, the cellulosic filler is a
wood flour. Wood flours are widely available materials produced by
pulverizing various wood residues obtained from commercial
operations, e.g., sawdust, using hammer mills or other suitable
equipment to reduce particle size. Wood flours are typically
classified based on the size of screen mesh through which the
material will pass and 30 to 150 mesh materials are most commonly
used.
[0042] In another highly useful embodiment, the matrix polymer is
HDPE or a mixture comprised of a majority of HDPE and one or more
other polyolefins, preferably polyethylene, resins.
Reclaim/recycled resins may also be included in the composites.
HDPEs and HDPE mixtures employed for these applications generally
have densities from 0.940 to 0.970 g/cm.sup.3 and, more preferably,
from 0.945 to 0.965 g/cm.sup.3.
[0043] To demonstrate the maleation process of the invention, the
following experiment was conducted using a distillation residue
obtained from a commercial two-stage HMW HDPE polymerization
process wherein ethylene-butene-1 copolymer was produced in hexane
using a high activity titanium catalyst and organoaluminum
co-catalyst. As part of the operation, hexane coming off of the
centrifuges used to recover the HMW HDPE was treated with octanol
to deactivate the catalyst and then distilled and purified for
recycle in the process. Residue, i.e., still bottoms, recovered
from this distillation was employed for the example. The solid wax
distillation residue contained 8 wt. % hexane, 0.5 wt. % catalyst
residues, 6 wt. % HMW HDPE and 85.5 wt. % low molecular weight
polyethylene polymers (M.sub.n less than 30,000) and trace amounts
(less than 400 ppm) octanol.
[0044] The solid wax residue was transferred to a glass reaction
vessel and heated to 120.degree. C. under a blanket of flowing
nitrogen with stirring (340 rpm) for approximately 30 minutes to
remove the hexane. After completion of this devolatilization step,
the amount of residual hexane was less than 0.01 wt. %.
[0045] The temperature of the molten mixture was then increased to
140.degree. C. and 3 wt. % maleic anhydride added while continuing
the stirring. After the maleic anhydride was uniformly dispersed
throughout the molten mixture, 3 wt. % dibenzoyl peroxide was added
and the mixture reacted for 20 minutes at 140.degree. C. with
stirring. After cooling the product was ground.
[0046] Analysis of the product by FTIR showed it to contain 1.8 wt.
% bound maleic anhydride and to be substantially free of unreacted
peroxide and unreacted maleic anhydride. The maleated product had a
waxy appearance and two DSC melting peaks (at 82.0.degree. C. and
115.8.degree. C.). The Brookfield viscosity at 150.degree. C. (20
rpm) was 1300 cP.
[0047] Additionally, the maleated product obtained from the
above-described procedure exhibited unexpected and highly desirable
viscometric behavior under conditions of shear such as may be
encountered during processing. Whereas typical commercial maleated
waxes exhibit viscosities which are essentially shear independent,
i.e., complex viscosity (P) remains essentially unchanged as the
shear rate (frequency) is varied, the maleated products produced by
the process of the invention using distillation residues containing
both low and high molecular weight polymer species exhibits shear
dependent viscosity.
[0048] This is apparent from the dynamic complex viscosity data
tabulated below. The rheological data were determined using a
Rheometrics ARES rheometer at 130.degree. C. in the parallel plate
mode (plate diameter 50 mm). Complex viscosities were determined
for a commercial maleated wax and the maleated product of the
invention in the frequency sweep mode at frequencies (shear rates)
ranging from 2.51 to 398 rad/sec. The commercial wax (EPOLEN C-18P)
is a maleic anhydride-modified low molecular weight polyethylene
(Acid Number 2; M.sub.n 5700; 150.degree. C. Brookfield viscosity
4000 cP).
TABLE-US-00001 Complex Viscosity (P) Maleated Maleated Shear Rate
Product of Invention Commercial Product 2.51 (low shear) 127.3 71.8
10 81.3 68.5 100 31.4 67.2 398 (high shear) 16.3 67
[0049] The unexpected difference in viscosity response at varying
shear rates for the two products is apparent from the above data.
The shear dependent viscosity of the maleated product obtained by
the process of the invention renders the product highly useful as a
coupling/compatibilizing agent for the manufacture of wood plastic
composites. Since WPC processes typically are high shear
operations, the lower viscosity of the maleated product of the
invention at high shear renders it readily compatible with the wood
flour filler due to the ease of wettability and facilitates
incorporation in the matrix polymer. The high viscosity at low
shear, which is evidence of molecular entanglements presumably as a
result of the presence of low and high molecular weight polymer
species, imparts enhanced mechanical strength to the finished WPC
product.
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